PHOTOSYNTHESIS & LIGHT REACTIONS (SONG) (SONG) (RAP) Obtaining Energy

Obtaining Energy Directly or indirectly, all of the energy in

living systems comes from the sun. Autotrophs must first capture light

energy from the sun. Autotrophs- a living thing that can

capture energy from sunlight or chemicals to make its own food

Is this an autotroph? If so, WHY?

Heterotrophs- a living thing that gets food by consuming, or eating, other living things.

Photosynthesis involves a series of chemical reactions where the product of one reaction is consumed in the next reaction.

Biochemical pathway- series of chemical reactions

Ke$ha gets complicated

Photosynthesis Divided into 2 stages:

(1) Light Reaction: Light energy is converted to chemical energy, stored in ATP and NADPH. NADPH (Nicotinamide Adenine Dinucleotide Phosphate) Energy carrier molecule

(2) Calvin Cycle: Forming organic compounds using CO2 and the chemical energy stored in ATP and NADPH.

Formula:

crash course 10 min clip

(1)Light Reaction Must absorb light in chloroplasts- organelles

found in cells of plants and algae.

Light reactionstake place in thethylakoids.

Light and Pigments Visible Spectrum- array of colors,

ranging from red to violet. When light strikes an object, its colors

can be transmitted, reflected or absorbed.

Light and Pigments Pigments- compounds that absorb light.

We see the colors that are reflected or transmitted, not the ones being absorbed.

Chloroplast Pigments Membrane of thylakoid has several

pigments.

Chlorophylls are the most important.

Chlorophyll a- directly involved in light reactions of photosynthesis

Chlorophyll b assist chlorophyll a in capturing light energy, called an accessory pigment.

Chloroplast Pigments Chlorophyll a absorbs less blue light but more red light. Neither absorb much green light, instead they reflect and

transmit green light.

Why do leaves and plants look green?

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1. They contain large amounts of chlorophyll

2. They contain no chlorophyll

3. They do not absorb green light

4. They reflect blue light

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Plants Plants appear green because they

contain large amounts of chlorophyll, which reflects or transmits most of the green light it intercepts.

Carotenoids Pigments in the thylakoid membrane

that aid in photosynthesis. Absorb blue and green, reflect yellow

orange and red, why leaves appear orange in color

In the fall, plants lost their chlorophylls and the leaves

Converting light energy to chemical energy

Chloroplast will capture the light and it must be converted into chemical energy.

Oxygen is given off during this reaction

Photosystem- cluster of chlorophyll and other pigment molecules that harvest light energy

Light Reaction Begins with absorption of light by

chlorophyll a and accessory pigments in the thylakoids.

Electrons leave chlorophyll a to travel along electron transport chains, producing NADPH.

Water is split and oxygen is released as the byproduct of photosynthesis.

Oxygen is produced at what point during photosynthesis?

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93%1. When CO2 is

fixed2. When water is

split3. When ATP is

converted

Photosynthesis- Light Reaction

Used Produced

Light Reaction

Light, Water, protons and electrons from water, NADP+, ADP

Oxygen, ATP, NADPH

The following is used in photosynthesis

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1. Oxygen2. ATP3. Water4. Carbohydrates

Making ATP Chemiosmosis-

synthesis of ATP

Movement of protons into the stroma of the chloroplast

From high concentration to low

(2)Calvin Cycle_C3 plants do this

Series of enzyme-assisted chemical reactions that produces a three-carbon sugar.

Carbon fixation- incorporating CO2 into organic compounds

3 CO2 molecules enter the Calvin Cycle. This cycle occurs in the stroma of chloroplasts.

Calvin CycleUsed Produced

Calvin Cycle ATP, CO2, NADPH, RuBP (ribulose biphosphate)

Organic Compounds (amino acids, lipids, and carbohydrates)NADP+, ADP

The following is produced in the Calvin Cycle

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97%1. ATP2. Carbohydrates3. Co24. Water

Calvin Cycle- Alternative Pathways Alternative way to fix carbon

Plants lose water through small pores called stomata

Stomata are a passageway for CO2 to enter and O2 to leave the plant

The complicated version....clip 5min

C4 Pathway and CAM Pathway Allows certain plants to fix CO2 into four

carbon compounds C4 have stomata partially closed during

the hottest part of the day (corn and sugar cane)

CAM- water-conserving, take in carbon at night and release it during the day. (cactuses and pineapples) CAM plants lose less water than C4 AND C3

plants

Factors that affect photosynthesisLight Intensity-Rate of photosynthesis increases as light intensity increases while exciting electrons. When all the electrons have been excited, the rate stays level.

Temperature-Increasing temperature accelerates the rate of photosynthesis. The rate peaks at the temperature where enzymes that catalyze reactions become ineffective.

Carbon Dioxide Levels -Increased levels will stimulate photosynthesis and then it will level off. SEE PG 124 for graphs

Which of the following describes light intensity in regards to rate of photosynthesis?

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1. As light increases, the rate increases and then levels off.

2. As light increases the rate decreases.

3. As light decreases, the rate increases.

4. As light increases the rate continues to increase.